Ukraine is expected to be discussed on the sidelines of the Paris meeting on Iraq Monday.

A senior U.S. State Department official says Secretary John Kerry will have pull-asides with several foreign ministers to review developments. The official told reporters travelling with the secretary that "It appears the Russians are treating the Donetsk border as their own."

The first trucks in a Russian aid convoy crossed into eastern Ukraine in the early hours of Saturday carrying relief goods to the embattled city of Luhansk.

The Organization for Security and Cooperation in Europe (OSCE), which has monitors in eastern Ukraine, reported that the first few trucks in the convoy of 216 vehicles received a cursory inspection by Russian border guards and customs services, but the rest were not checked. No Ukrainian or Red Cross officials inspected the convoy. All the trucks returned to Russia Saturday evening.

The Ukrainian military said it had beaten back a rebel attack on the airport at Donetsk, and later Saturday Western journalists confirmed the reports of heavy fighting at the airport. Ukraine authorities said the facility first drew rebel artillery fire late Friday, a move threatening a shaky cease-fire signed by envoys from the rebel movement, the Kyiv government, European monitors and Russia.

As events on the ground unfolded, Ukraine's Prime Minister Arseniy Yatsenyuk accused Russian President Vladimir Putin of deliberately maintaining a state of war in Ukraine, with the aim of destroying it as an independent country.

In an address to an international forum in Kyiv, Yatsenyuk also praised the new wave of economic sanctions imposed on Russia by the West. He spoke a day after the European Union and the United States expanded sanctions targeting Russia's energy, financial and defense sectors in a new push to punish Moscow for its role in the Ukraine crisis.

Western governments accuse Moscow of supplying military hardware and fighters to pro-Russian separatists seeking autonomy from Kyiv in Russian-speaking regions near the border. The Kremlin also stands accused of supplying the missile battery used to down a Malaysian airliner as it flew through Ukrainian airspace in mid-July. All 298 people on board perished.

Russia has repeatedly denied involvement, and has ordered a series of retaliatory sanctions as international pressure against Moscow intensifies.